Its amazing to me how a simple and common sense rule can cause so much confusion.
The capability must exist to externally disarm all pyrotechnic devices on-board the rocket.
In this context, disarm means the ability to physically break the connection between a
pyrotechnic system and its power source.
How to do this shouldn't be a matter of L3CC analysis. You ask your altimeter manafacturer "Does disconnecting power to the altimeter break the power to the pyrotechnic devices?". Two possible answers:
Answer 1. Yes it does. -> Then show this to your L3CC and use a single altimeter switch per altimeter if you desire.
Answer 2. No it doesn't because the altimeter has persistent energy storage on-board. -> Then you need a switch to break the pyro circuit. Even if you belong to TRA.
What is persistent energy storage onboard? Magic? A battery? A capacitor? I will concede that a device with two batteries, one to power the altimeter and one for the pyro circuit could still have power going through the ematch circuit for continuity detection. Two come to mind immediately. The out of production Parrot altimeter that had two screw switches, one for the onboard battery to power the unit, one for a 9V pyro battery. I believe the pyro battery was in the circuit for continuity purposes even if the altimeter was off. Was also a PITA to screw both switches in on such a small sized altimeter. The ARTS 2 has two battery capability but only one switch. I don't know if both batteries are off with the one switch connection.
The EggTimer altimeter in one of it's forms has separate batteries. One for the electronics, one or two additional for the pyro. Now current is going through the pyro circuit with the altimeter off. How do I know? I had LEDs attached for testing and there is a faint glow with the pyro battery attached and the altimeter shut off. It is the limited current going through for continuity even with the altimeter turned off. Is this a safety hazard? NOOOOO!!!! Is it a nuisance?
Can be. It's a nuisance because one CAN'T preload a rocket ahead of time without the pyro battery being drained (without a switch) If I was going to do that
with an EggTimer, I'd use use a DPST switch to turn the pyro batt and the altimeter on/off at the same time.
If one connects the pyro battery directly at the launchsite then goes and flies, no problem. Letting the rocket sit for weeks could lead to a drained pyro battery. The ET would beep a fault on the pad and in that case if the flier ignored it, it would be a ballistic flight. (Safety hazard if one ignores a pad altimeter fault)
Oh, I did put live matches on the ET circuit with the pyro battery and guess what? Nothing happened.
John, that logic is impaired and has nothing to do with safety. An ET with a "live" pyro battery is no more dangerous than one that has no pyro battery.
It is not going to "blow" when one connects up the ematches. I simply recommend a DPST switch to make sure maximal juice is there when ready to fly.
I know the old NAR rule of switches on every charge is gone now and that's fine. Was just a multi-point failure risk and further reason to consider TRA for L3 flight (that isn't there anymore of course). If one doesn't want to worry about it, use MAWD's, Stratologgers, Ravens or any of the single battery altimeters out there. Kurt